Conventionally, as a measurement method of urea nitrogen in a body fluid, a method called a dry method (dry chemistry) has variously been proposed to attempt simplification and acceleration of measurement and to eliminate individual difference of a measurer. The typical method is to use an integral multilayer analysis element comprising a reagent layer containing urease and an alkaline buffer, an indicator layer that detects gaseous ammonia, and a permselective layer that selectively permeates only the gaseous ammonia, interposed between those. For example, Patent Document (JP-A-52-3488) discloses an integral analysis element basically having the above-described multilayer structure. This analysis element uses a hydrophobic polymer thin film as a permselective layer of an ammonia gas.
Patent Document 2 (JP-A-58-77661) discloses an integral multilayer analysis material for analyzing ammonia or an ammonia formation substrate in a liquid sample, comprising a transparent support having an indicator layer for gaseous ammonia, a liquid blocking layer, a reagent layer containing an alkaline buffer and if necessary a reagent that can product ammonia by reacting with a substrate, and a spreading layer, integrally adhesion laminated thereon in this order, characterized in that the liquid blocking layer comprises a porous substance, and constitutes air holes that substantially block a liquid sample and permeates a gaseous ammonia under use conditions. In this multilayer analysis material, an integral multilayer analysis element that uses a membrane filter as a permselective layer to improve adhesion to the indicator layer and to attempt sensitization is disclosed.
Besides, Patent Document 3 (JP-A-4-157363) discloses an integral multilayer analysis element for analyzing ammonia or an ammonia product, having further increased color optical density, low color optical density of background and further high measurement accuracy using a polyvinyl alkyl ether that does not substantially contain ammonia or ammonium ions in an undercoat layer of a support, or using a polyvinyl alkyl ether in a binder of an indicator layer. Further, Patent Document 4 (JP-A-4-157364) discloses an integral multilayer analysis element for analyzing ammonia or an ammonia product, having further increased color optical density, low color optical density of background and further high measurement accuracy by containing poly(N-vinylpyrrolidone) in a porous spreading layer, not substantially containing ammonia in an ammonia formation reaction reagent layer, and using a binder that does not generate ammonia at pH of about 9.0 or higher and does not change binder performance. Further, Patent Document 5 (JP-A-2002-122585) discloses an integral multilayer analysis element for analyzing ammonia or an ammonia product in a liquid sample, comprising a transparent support having an indicator layer containing a reagent that generates a detectable change by gaseous ammonia, a liquid blocking layer that passes gaseous ammonia, a reagent layer containing an alkali buffer and if necessary a reagent that can produce ammonia by reacting with a substrate, and a spreading layer, integrally adhesion laminated thereon in this order, characterized in that the liquid blocking layer comprises at least two layers of porous films.
Patent Document 1: JP-A-52-3488
Patent Document 2: JP-A-58-77661
Patent Document 3: JP-A-4-157363
Patent Document 4: JP-A-4-157364
Patent Document 5: JP-A-2002-122585